A typical implantable tissue stimulator such as a device for electrically stimulating the heart at predetermined time intervals comprises a battery, an output circuit for providing tissue stimulation pulses and a volatile memory and control circuit for controlling frequency and other parameters provided by the tissue stimulator. It is well known in the medical sciences that the frequency provided by a tissue stimulator is extremely critical to the health of a patient. In programmable tissue stimulators these pulses are controlled by a programmable memory which contains information predetermined with respect to pulse requirements of a particular patient. A problem with these system utilizing a volatile memory is that the information contained therein can be affected if the battery voltage drops below a certain critical level, this altered information having a deleterious effect on a patient due to its control of the tissue stimulation pulse characteristics. Conventional tissue stimulators have attempted to alleviate the problem in several ways, one of which has been to inactivate the output circuit if the battery output voltage falls below a predetermined level. However this results in an immediate removal of pulses which in severe cases could result in extreme discomfort and even death to the patient prior to the time that the battery could be removed and replaced.